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Peter Dahl

Senior Principal Engineer

Professor, Mechanical Engineering





Research Interests

Underwater Acoustics, Acoustic Remote Sensing


Dr. Dahl is a Senior Principal Engineer in the Acoustics Department and a Professor in the University of Washington's Department of Mechanical Engineering. Professor Dahl's research is in areas of acoustics with primary focus on underwater sound. Examples of his research include underwater acoustic remote sensing, the acoustics of underwater explosions, acoustic scattering and reflection from the sea surface and sea bed, vector acoustics, underwater ambient noise and methods to reduce underwater industrial noise.

He has conducted several ocean-going experiments involving underwater acoustics, including the Asian Seas International Acoustics Experiment (ASIAEX), sponsored by the U.S. Office of Naval Research, in the East China Sea involving the U.S., China and Korea and for which he was U.S. chief scientist.

Professor Dahl is a Fellow of the Acoustical Society of America, has served as the chair of its technical committee on underwater acoustics (2002–2005), on its Executive Council (2008–2011), and has recently completed service as Vice President of the Acoustical Society of America.

Department Affiliation



Ph.D. Ocean Engineering, Massachusetts Institute of Technology, 1989


2000-present and while at APL-UW

Observations of water column and bathymetric effects on the incident acoustic field associated with shallow-water reverberation experiments

Dall'Osto, D.R., and P.H. Dahl, "Observations of water column and bathymetric effects on the incident acoustic field associated with shallow-water reverberation experiments," IEEE J. Ocean. Eng., 42, 1146-1161, doi:10.1109/JOE.2017.2717661, 2017.

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1 Oct 2017

As a part of the 2013 Targets and Reverberation Experiment (TREX13), measurements of the acoustic field generated by a source used in midfrequency (1.8–3.6 kHz) reverberation experiments are studied at 5 and 6 km range. The TREX13 reverberation sources were placed off the coast of Panama City, FL, USA, in waters ~20 m deep, and data discussed here are from a 2-h period in the late afternoon on April 28, 2013. The observed coda of the source signal is partitioned into an initial primary arrival, and a distinct second arrival delayed by roughly 2 s. Characteristics of the two arrivals are studied in terms of the effective number of modes, interference features, and the direction of acoustic intensity, which was directly measured by a vector sensor located at 5 km range. A shift in frequency within the primary arrival is observed over the 2-h measurement period. Frequency shifts are related to a change in range of dislocations, defined as points of complete destructive interference in the acoustic field, that modulate with tidal variation in the sound-speed profile. Precise frequencies are identified with the vector property called circularity, a nondimensional measure of acoustic intensity curl, that is maximal within the vortex-like intensity field within a dislocation. Using the waveguide invariant β, the frequency shift is used to estimate the tidal change in the thermocline depth. These interference features are absent in the second arrival, which is postulated to be an acoustic path horizontally refracted by the gently sloping bathymetry (~0.4°) forming the coastal environment. A description of the refraction using modal rays is developed, and the transition of the mode from being trapped to leaky is handled as a transition to a virtual mode near the cutoff depth. Models of the primary and refracted arrivals are presented to support the conclusions.

On the underwater sound field from impact pile driving: Arrival structure, precursor arrivals, and energy streamlines

Dahl, P.H., and D.R. Dall'Osto, "On the underwater sound field from impact pile driving: Arrival structure, precursor arrivals, and energy streamlines," J. Acoust. Soc. Am., 142, 1141, doi:10.1121/1.4999060, 2017.

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1 Aug 2017

Underwater noise from impact pile driving is studied through measurements using a vertical line array (VLA) placed at range 120 m from the pile source (water depth 7.5 m) over which bathymetry varied gradually increasing to depth 12.5 m at the VLA. The data were modeled assuming the pile impact produces a radial expansion that acts as sound source and propagates along the pile at supersonic speed. This leads to the conceptualization of the pile as a discrete, vertical line source for which frequency- and source-depth-dependent complex phasing is applied. Dominant features of the pressure time series versus measurement depth are reproduced in modeled counterparts that are linearly related. These observations include precursor arrivals for which arrival timing depends on hydrophone depth and influence of a sediment sound speed gradient on precursor amplitude. Spatial gradients of model results are taken to obtain estimates of acoustic particle velocity and vector intensity for which active intensity is studied in the time domain. Evaluation of energy streamlines based on time-integrated active intensity, and energy path lines based on instantaneous (or very-short-time integrated) active intensity reveal interesting structure in the acoustic field, including an inference as to the source depth of the precursor.

Observations of sea-surface waves during the 2013 Target and Reverberation Experiment (TREX13) and relation to midfrequency sonar

Dahl, P.H., and D.R. Dall'Osto, "Observations of sea-surface waves during the 2013 Target and Reverberation Experiment (TREX13) and relation to midfrequency sonar," IEEE J. Ocean. Eng., 42, 250-259, doi:10.1109/JOE.2016.2597718, 2017.

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1 Apr 2017

As part of the 2013 Target and REverberation eXperiment (TREX13), which took place off the coast of Panama City, FL, USA, directional wave measurements were made using two directional wave buoys separated in range by 5 km. The purpose of these measurements was to provide environmental support for the interpretation of reverberation and other active sonar experiments that were part of TREX13. During the measurement period between April 22 and May 17, 2013 exclusive of a period of nondeployment May 2–6, 2013, the root-mean-square (rms) wave height H varied over the range 0.03–0.33 m, holding a median value of 0.11 m; the wind speed varied from ~1 to 10 m/s with a median value of 4.7 m/s, and the rms wave slope averaged over all directions varied from 0.01 to 0.10 with median value of 0.05. These parameters are placed in the context of midfrequency sonar propagation and reverberation prediction. One buoy operated the entire period, with the second buoy operating simultaneously over a four-day overlap period, during which there was excellent agreement between H and wave slope in two orthogonal directions, a finding relevant to describing the sea surface as spatially invariant, or homogeneous, for purposes of sonar modeling. The analysis of energy-weighted mean direction illustrates how the wave field was generally composed of a mixture of swell and wind-generated waves; in cases of purely wind-generated waves the effect of a limited fetch was also shown.

More Publications


Airborne Acoustic Particle Motion Sound Meter

Record of Invention Number: 48135

David Dall'Osto, Peter Dahl


1 Aug 2017

Pile with Sound Abatement

Patent Number: 9,617,702

Peter Dahl, John Dardis II, Per Reinhall

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11 Apr 2017

A noise-attenuating pile comprising a pile driving shoe, an outer tube that engages the pile driving shoe, and an inner member that extends through the outer tube and engages the pile driving shoe, wherein the pile is configured to be installed in sediment or other suitable material by driving the inner member with a pile driver, without directly impacting the outer tube, such that the radial outer tube is substantially insulated from the radial expansion waves generated by the pile driver impacting the inner member. In some piles, one of the inner member and the outer tube are removable after installation. In some piles, a seal is provided in a lower end of the channel defined between the inner member and the outer tube, which may be biodegradable, or may be an inflatable bladder, for example.

Pile to Minimize Noise Transmission and Method of Pile Driving

Patent Number: 8,622,658

Per G. Reinhall, Peter Dahl

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7 Jan 2014

A pile and method for driving a pile includes a pile having a structural outer tube, and an inner member disposed generally concentrically with the outer tube. The outer tube and inner member are fixed to a driving shoe. The pile is constructed and driven such that the pile driver impacts only the inner member. The impact loads are transmitted to the driving shoe to drive the pile into the sediment, such that the outer tube is thereby pulled into the sediment. In a particular embodiment the outer tube is formed of steel, and the inner member also comprises a steel tube. In an alternative embodiment one or both of the inner member and the outer tube are formed of an alternative material, for example, concrete. In an embodiment, the outer tube has a recess that captures a flange on the inner member. In an embodiment the outer tube is attached to the inner member with an elastic spring.

More Inventions

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center